In some motor vehicle climate control systems, a thermal-adsorption heat pump may be used instead of a compressor-driven heat pump. Thermal-adsorption heat pumps use an adsorbent chemical (e.g. zeolite, silica gel, activated carbons) rather than a mechanical compressor, and are driven by thermal energy (such as waste exhaust heat) rather than mechanical work.
One cycle of operation of a thermal-adsorption heat pump includes the adsorption of a refrigerant, e.g. water, onto adsorbent material, e.g. zeolite (during what is referred to herein as “adsorbing mode”), and the subsequent desorption of the refrigerant from the adsorbent (during what is referred to herein as “desorbing mode”). During the adsorbing mode, the adsorbent is actively cooled to effect the adsorption, for example via coolant circulating in tubes thermally coupled with the adsorbent. The cooling of the adsorbent creates suction, which draws vaporized refrigerant onto the adsorbent.
Typically, thermal-adsorption heat pumps include two adsorber chambers which alternate between adsorption and desorption, and which are thermally coupled with a dedicated condenser and evaporator. For example, US 2008/0066473 describes an adsorption heat pump for providing air conditioning to a motor vehicle having two adsorber chambers, which are each connected to a condenser and an evaporator. Both of the adsorber chambers are coated with a sorbent. The adsorber chambers, condenser, and evaporator are enclosed by a vacuum shell. The system achieves quasi-continuous air conditioning by operating such that the first adsorber chamber is adsorbed or desorbed alternately, and simultaneously the second adsorber chamber is desorbed or adsorbed, respectively. During adsorption of an adsorber chamber, the adsorber chamber communicates with the evaporator but not the condenser, whereas during desorption of an adsorber chamber, the adsorber chamber communicates with the condenser but not the evaporator. The adsorption heat pump is driven by engine waste heat, and operates in conjunction with one or more of an air cooler, recooling unit, and heat pipe(s), depending on the embodiment, to provide cooling to the passenger cabin.
In other conventional air-conditioning systems, two pairs of heat exchangers may be used, where one pair of heat exchangers is operated in a desorbing mode while the other pair is operating an in adsorbing mode. The pair operating in the adsorbing mode at a given time provides cooling.
In contrast with the above-described systems, the inventors herein have identified an air-conditioning system incorporating a thermal-adsorption heat pump which does not require a dedicated evaporator and condenser, and which does not require two pairs of heat exchangers. That is, the inventors herein have recognized that a first heat exchanger comprising adsorbent material may fluidly communicate with a second heat exchanger not comprising adsorbent material inside a vacuum enclosure, and the second heat exchanger may perform the same functionality as a dedicated evaporator and condenser when used in conjunction with a radiator and an air-conditioning core comprising phase changing materials. In one example, a method for an air-conditioning system includes, during engine operation, alternating between a desorbing/condensing mode and an adsorbing/evaporating mode. The desorbing/condensing mode, which is alternatively referred to as simply a desorbing mode herein for the sake of brevity, comprises circulating coolant between an engine waste heat recovery system and a first adsorbing/desorbing heat exchanger while circulating coolant between a radiator and a second heat exchanger, whereas the adsorbing/evaporating mode, which is alternatively referred to as simply a adsorbing mode herein for the sake of brevity, comprises circulating coolant between the radiator and the first heat exchanger while circulating coolant between an air-conditioning core comprising phase changing materials and the second heat exchanger. Accordingly, during the adsorbing mode, the radiator supplies ambient-temperature coolant to the first heat exchanger, which effects adsorption of vapor at the adsorbent material in the first heat exchanger and corresponding suction of vapor from the second heat exchanger to the first heat exchanger. Suction of vapor at the second heat exchanger cools the coolant circulating between the second heat exchanger and the air-conditioning core, such that a blower may push ambient or recirculated air past the air-conditioning core to the cabin to cool the cabin. Meanwhile, the phase changing materials in the air-conditioning core freeze. In contrast, during the desorbing mode, waste heat supplies hot coolant to the first heat exchanger, which causes the adsorbent material to release (desorb) vapor, which then condenses in the second heat exchanger. The heat of condensation is transferred from the second heat exchanger to the radiator via coolant and rejected to the environment. In the air-conditioning core, melting phase changing materials exchange heat with ambient or recirculated air, and the cooled air is directed to the cabin. Thus, a special technical effect of the air-conditioning system described herein is the ability to provide cooling using a single pair of thermally-driven heat exchangers in conjunction with an air-conditioning core incorporating phase changing materials and without the need for a dedicated evaporator and condenser.
In addition to other advantages associated with non-compressor-driven air-conditioning systems (e.g., reduction of air-conditioning accessory loads), providing air conditioning in the manner described above may reduce costs by reducing the size of the air-conditioning system (e.g., as the system does not include a dedicated evaporator and condenser or a second pair of heat exchangers). Further, control may be simplified relative to systems requiring two pairs of heat exchangers.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.